A. Technical Field
The present invention relates to lighting devices, and more particularly, to ultraviolet light panels for generating light with enhanced intensity uniformity.
B. Background of the Invention
Light (Display) panels are widely used in various devices, such as mobile phones, notebooks, desktop monitors, notepads, and so on. Typically, a display panel has a backlight source that provides light for the display panel. The state-of-the-art display panels adopt high-efficiency InGaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) as backlight sources taking advantage of the up to 70% electricity-light conversion efficiency. The basic function of a light panel is to transform the LED's point light source into a uniform areal light source. As such, one of the challenges that a device designer encounters is to control the beam uniformity across the entire display panel. If the light intensity on a portion of the display panel is brighter and/or darker than the rest, not only the quality of the images displayed on the display panel is deteriorated, but also the lifetime of the device is shortened. Further, ultraviolet (UV) light panels can be realized by utilizing ultraviolet light sources as backlight. For example, AlGaN MQW LEDs emitting at wavelengths in the range of 240-365 nm can be used as ultraviolet light panel backlight sources for germicidal and medical applications. In this case, if the device is used to sterilize harmful germs/virus over a target area, a portion of the target area treated by the darker portion of the panel may not be sterilized to the intended level. Another challenge for a quality light panel is to reduce light loss during the light redistribution process. This is most critical for a UV light panel, since UV light loss is severer compared to visible light due to its shorter wavelength and higher photon energy resultant stronger scattering and absorption coefficient.
FIG. 1A shows a schematic diagram of a conventional display panel 1. As depicted, the light sources, 1s, generate light that passes through the lightguide, 1l, prism sheet, 1p, and diffuser 1d, where the lightguide, prism sheet and diffuser convert the light beams from the discrete light sources 1s into the light 11 spread over the entire area of the panel. The display panel 1 has several drawbacks. First, since the light beams from the light sources 1s pass through multiple components, some portion of the light is absorbed by these components, reducing the overall efficiency of the panel. Second, the stacked components increase the form factor of the display panel 1, increasing the manufacturing cost of the panel and the form factor of the device that uses the panel.
FIG. 1B shows another conventional display panel 2. As depicted, the light sources, 2s, generate light beams that pass through the lightguide, 2l, prism sheet, 2p, and diffuser 2d, where the lightguide, prism sheet and diffuser convert the light beams from the discrete light sources into the light spread over the entire area of the panel. Unlike the display panel 1, the lightguide 2l steers the direction of the light beams by about 90 degrees. As the light sources 2s are disposed on one side of the lightguide 21 to thereby reduce the overall thickness of the display panel 2, the reduction of thickness is obtained at the expense of area increase. Thus, the display panel 2 has the similar problems as the display panel 1.
Therefore, a better solution is needed to provide light panels with enhanced intensity uniformity and reduced form factors; moreover, a ultraviolet light panel is needed for transforming point or linear ultraviolet light source into uniform areal light source with minimal light loss.